A Casing Force Prediction Method with a Missing of Cement Sheath Based on Cementing Displacement Efficiency

Due to the low cementing displacement efficiency(CDE), the cement sheath around the casing is prone to be missing, and the casing deformation problem occurs frequently during the subsequent hydraulic fracturing process. Aiming at this problem, a casing force prediction method is proposed in this paper. Firstly, a prediction model of replacement efficiency was established to analyze the influence of different factors on CDE, which can predict the geometry of the cement sheath at different well depths, and is used to characterize where and to what extent the cement sheath is missing in the wellbore. Subsequently, a casing-cement sheath-formation finite element model was established to study the distribution law of casing stress at different degrees of cement sheath missing and calculate the corresponding casing safety coefficient. Based on the safety coefficient, it can be judged whether the casing at the depth of the current well meets the requirements for safe production. Taking well A in Changqing oilfield in China as an example, the method was utilized. The results show that the upper well section is highly susceptible to casing deformation due to the low CDE, the large degree of missing casing, and the low safety coefficient. According to the method proposed, field workers can predict the casing stress in advance. 1. INTRODUCTION It is well known that cementing quality has a large impact on wellbore integrity (Yan, et al., 2018; Liu, et al., 2022). Due to the low cementing displacement efficiency(CDE) during cementing, the cement ring around the casing is prone to defects, and the casing deformation problem occurs frequently in the subsequent hydraulic fracturing process (Li, et al., 2019; Yan, et al., 2019; Jiang, et al., 2020; Liu, et al., 2023). Casing eccentricity and low displacement are the main reasons for low CDE. There are more research results on the displacement efficiency, and most of them are calculated by numerical simulation software (Zulqarnain, et al., 2016; Yang, et al., 2021; Xue, et al., 2022). However, fewer research results have been applied to the field of cement ring integrity(Vefring, et al., 1997; Mirjalili, et al., 2017).